1. Field of the Invention
This invention relates to a process for producing alkenyl ethers. More particularly it relates to a process for producing an .alpha.,.beta.-unsaturated ether, an unsaturated ether having conjugated double bonds, a hydroxyalkenyl ether or a hydroxyalkenyl ether having conjugated double bonds.
2. Description of the Related Art
As to conventional processes for producing .alpha.,.beta.-unsaturated ethers, for example the following synthesis is disclosed in J. Org. Chem., 23, 670 (1958): ##STR4##
Namely, from 2-ethylhexylaldehyde of the formula 3 and 2-ethylbutyl alcohol of the formula 4 is prepared 1-chloro-2-ethylhexyl-2'-ethylbutyl ether of the formula 5 , which is converted into 1-acetoxy-2-ethylhexyl-2'-ethylbutyl ether of the formula 6 , from which acetic acid is removed in gas phase at 230.degree. C., to prepare 2-ethylhexenyl-2-ethylbutyl ether of the formula 7 . In general, most of production processes of .alpha.,.beta.-unsaturated ethers have been carried out by subjecting acetals to catalytically thermal decomposition in gas phase at a high temperature of 300.degree. to 800.degree. C., as disclosed in Japanese patent application laid-open No. Sho 57-185232/1982, etc.
However, such conventional production processes of .alpha.,.beta.-unsaturated ethers have drawbacks of requiring two or three steps starting from aldehydes and also requiring high temperatures in gas phase reaction.
Further, as to the production process of an unsaturated .alpha.,.beta.-ether having conjugated double bonds, the following synthesis is disclosed in J. Polym. Sci., Part A-1, Vol. 9, 164, 1971: ##STR5##
Namely, from an unsaturated aldehyde and an alcohol is prepared a 3-alkoxyacetal in the presence of an alkali catalyst, followed by removing the alcohol from the acetal in liquid phase in the presence of an acidic catalyst to prepare an unsaturated ether having conjugated double bonds.
However, this synthesis also requires two stages.
Thus, a commercial production process wherein the number of steps starting from aldehydes is small and the reaction is carried out under mild conditions has been desired.
Next, the prior art of production process of hydroxyalkenyl ethers among unsaturated ethers having conjugated double bonds will be described.
A synthesis of a vinyl ether among hydroxyalkenyl ethers is disclosed in U.S. Pat. No. 3,429,845 or Ann. Chem., 601, 81 (1956). In this synthesis, an alkane diol is added to acetylene. However, according to such a process, high temperature and high pressure are required for the reaction, and byproducts such as a divinyl compound (CH.dbd.CHOAOCH.dbd.CH) or a cyclic acetal are formed in a large quantity; hence the process is unsuitable as a commercial means.
On the other hand, a process of reacting ethanediol with an alkyl vinyl ether in the presence of mercuric acetate is disclosed in J. Am. Chem. Soc., 79, 2828 (1957). According to this process, main products are dioxolan and divinyl ether and 2-hydroxyethyl vinyl ether forms as a byproduct; hence it is impossible to employ this process as a production process of hydroxyalkenyl ethers.
Since such a hydroxyalkenyl ether having conjugated double bonds has conjugated double bonds, the ether can be expected as a functional monomer. Such a hydroxyalkenyl ether having conjugated double bonds is a novel substance.
As apparent from the foregoing, the object of the present invention is to provide a process for producing alkenyl ethers from an aldehyde at one step and under mild reaction conditions.